Perivascular support of human hematopoietic stem/progenitor cells

Hematopoietic stem and progenitor cells (HSPCs) emerge and develop adjacent to blood vessel walls in the yolk sac, aorta-gonad-mesonephros region, embryonic liver, and fetal bone marrow. In adult mouse bone marrow, perivascular cells shape a "niche" for HSPCs. Mesenchymal stem/stromal cells (MSCs), which support hematopoiesis in culture, are themselves derived in part from perivascular cells. In order to define their direct role in hematopoiesis, we tested the ability of purified human CD146⁺ perivascular cells, as compared with unfractionated MSCs and CD146^– cells, to sustain human HSPCs in coculture. CD146⁺ perivascular cells support the long-term persistence, through cell-to-cell contact and at least partly via Notch activation, of human myelolymphoid HSPCs able to engraft primary and secondary immunodeficient mice. Conversely, unfractionated MSCs and CD146^– cells induce differentiation and compromise ex vivo maintenance of HSPCs. Moreover, CD146⁺ perivascular cells express, natively and in culture, molecular markers of the vascular hematopoietic niche. Unexpectedly, this dramatic, previously undocumented ability to support hematopoietic stem cells is present in CD146⁺ perivascular cells extracted from the nonhematopoietic adipose tissue (read more)

A Single Dose of Rituximab Does Not Deplete B Cells in Secondary Lymphoid Organs but Alters Phenotype and Function

A single dose of the anti-CD20 monoclonal antibody rituximab induces a nearly complete B cell depletion in peripheral blood, but not in secondary lymphoid organs. Modulation of this remaining B cell population due to rituximab treatment may contribute to the therapeutic effects of rituximab. To assess the in vivo effects of rituximab we used lymph nodes (LNs) collected during renal transplant surgery in patients who had received rituximab 4 weeks earlier in preparation for an ABO-incompatible transplantation. Rituximab treatment resulted in a lower percentage of naïve (IgD⁺CD27⁻) and a higher percentage of switched memory (IgD⁻CD27⁺) B cells. Remarkably, transitional (CD24⁺⁺CD38⁺⁺) B cells were virtually lacking in the LNs of rituximab-treated patients. Moreover, LN-derived B cells from rituximab-treated patients produced different amounts of various Ig-subclasses after anti-CD40/IL-21 stimulation ex vivo. Finally, after stimulation of allogeneic T cells with LN-derived B cells from rituximab-treated patients, the proliferated T cells showed a decreased production of IL-17. In conclusion, after treatment with rituximab there remains a B cell population with different functional capacities. Consequently, the effect of rituximab on the immune response will not only be determined by the extent of B cell depletion, but also by the functional properties of the remaining B cells (read more)

The Effect of Rabbit Anti-Thymocyte Globulin on Human Mesenchymal Stem Cells

Background : Mesenchymal stem cells (MSCs) possess immunomodulatory properties which are of key interest for their application in autoimmunity and transplantation. In transplantation, administration of MSCs has shown promising results in preclinical models and has recently moved to clinical trials. Therefore it is important to study the interactions between MSCs and immunosuppressive drugs currently used in transplantation. We aimed to analyze the effect of rabbit anti-thymocyte globulin (rATG) MSCs.
Methods : MSCs were obtained from perirenal fat of kidney donors and exposed to ranging doses of rATG (Thymoglobulin®, Genzyme;0.5ug/ml-100ug/ml). Binding of rATG, effects on viability and susceptibility to be killed by cytotoxic lymphocytes as well as effects on their immunosuppressive potential of MSCs were tested.
Results : rATG binds dose-dependently to MSCs. This binding was associated with slightly impaired viability after 48 and 72 hours when compared to non-exposed MSCs. In contrast to non-treated MSCs, rATG pre-exposed MSCs were susceptible to be lysed by cytokine-activated CD8+ cytotoxic cells and NKT cells. The capacity of MSCs to suppress the proliferation of anti-CD3/CD28 activated CD4 and CD8 T cells was reduced by the presence of rATG in the culture.
Conclusion : rATG reduces the viability and anti-proliferative capacity of MSCs in a dose dependent manner and converts them into targets for CD8 T cells and NKT cell lysis (read more)

Efficacy of HLA-matched platelet transfusions for patients with hypoproliferative thrombocytopenia: a systematic review

BACKGROUND: HLA-matched platelets (PLTs) are widely used to transfuse patients but the effectiveness of HLA matching has not been well defined and the cost is approximately five times the cost of preparing the random-donor PLTs. The objective of this systematic review was to determine whether HLA-matched PLTs lead to a reduction in mortality; reduction in frequency or severity of hemorrhage; reduction in HLA alloimmunization, refractoriness, or PLT utilization; or improvement in PLT count increment in patients with hypoproliferative thrombocytopenia.
STUDY DESIGN AND METHODS: We conducted a literature search of MEDLINE, Cochrane Controlled Register of Clinical Trials, EMBASE, and PubMed databases to April 2012.
RESULTS: A total of 788 citations were reviewed and 30 reports were included in the analysis. Most studies did not include technologies currently in use for HLA typing or detection of HLA antibodies as 75% were conducted before the year 2000. None of the studies were adequately powered to detect an effect on mortality or hemorrhage. HLA-matched PLTs did not reduce alloimmunization and refractoriness rates beyond that offered by leukoreduction, and utilization was not consistently improved. HLA-matched PLTs led to better 1-hour posttransfusion count increments and percentage of PLT recovery in refractory patients; however, the effect at 24 hours was inconsistent.
CONCLUSION: The correlation of the PLT increment with other clinical outcomes and the effect of leukoreduction on HLA-matched PLT transfusion could not be determined. Prospective studies utilizing current technology and examining clinical outcomes are necessary to demonstrate the effectiveness of HLA-matched PLT transfusion (read more)

De Novo Donor-Specific HLA Antibodies Decrease Patient and Graft Survival in Liver Transplant Recipients

The role of de novo donor-specific HLA antibodies (DSA) in liver transplantation remains unknown as most of the previous studies have only focused on preformed HLA antibodies. To understand the significance of de novo DSA, we designed a retrospective cohort study of 749 adult liver transplant recipients with pre- and posttransplant serum samples that were analyzed for DSA. We found that 8.1% of patients developed de novo DSA 1 year after transplant; almost all de novo DSAs were against HLA class II antigens, and the majority were against DQ antigens. In multivariable modeling, the use of cyclosporine (as opposed to tacrolimus) and low calcineurin inhibitor levels increased the risk of de novo DSA formation, while a calculated MELD score >15 at transplant and recipient age >60 years old reduced the risk. Multivariable analysis also demonstrated that patients with de novo DSA at 1-year had significantly lower patient and graft survival. In conclusion, we demonstrate that de novo DSA development after liver transplantation is an independent risk factor for patient death and graft loss (read more)

Who is the better donor for older hematopoietic transplant recipients: an older-aged sibling or a young, matched unrelated volunteer?

Older patients are increasingly undergoing allogeneic hematopoietic transplantation. A relevant question is whether outcomes can be improved with a younger allele-level 8/8 HLA-matched unrelated donor (MUD) rather than an older HLA-matched sibling (MSD). Accordingly, transplants in leukemia/lymphoma patients age ≥50 years were analyzed comparing outcomes for recipients of MSD ≥50 (n = 1415) versus MUD <50 years (n = 757). Risks of acute graft-versus-host disease (GVHD) grade 2 to 4 (hazard ratio [HR], 1.63; P < .001), 3 to 4 (HR, 1.85; P < .001), and chronic GVHD (HR, 1.48; P < .0001) were higher after MUD compared with MSD transplants. The effect of donor type on nonrelapse mortality (NRM), relapse, and overall mortality was associated with performance score. For patients with scores of 90 or 100, NRM (HR, 1.42; P = .001), relapse (HR, 1.45; P < .001), and overall mortality (HR, 1.28; P = .001) risks were higher after MUD transplants. For patients with scores below 90, NRM (HR, 0.96; P = .76), relapse (HR, 0.86; P = .25), and overall mortality (HR, 0.90; P = .29) were not significantly different after MUD and MSD transplants. These data favor an MSD over a MUD in patients age ≥50 years (read more)

Partially Mismatched Transplantation and Human Leukocyte Antigen Donor-Specific Antibodies

The presence of donor human leukocyte antigen (HLA)-specific antibodies (DSA) increases engraftment failure risk in partially HLA-mismatched, or HLA-haploidentical, allogeneic marrow (alloBMT) transplantation. As pre-existing sensitization to HLA antigens is not well characterized among candidates for HLA-haploidentical alloBMT, we retrospectively evaluated both the incidence and relative strength of DSA in this patient population. Based on correlations of solid-phase antibody assays on the Luminex (Luminex, Austin, TX) platform with actual crossmatch tests, DSA were characterized as weak for results that were consistent with negative flow cytometric crossmatch results or as moderate-to-strong for results consistent with positive flow cytometric or cytotoxicity crossmatches. We evaluated 296 alloBMT candidates; 111 (37.5%) were female. DSA were detected in 43 (14.5%) candidates, mostly among female candidates (42.9% female versus 12.5% male). Moderate-to-strong DSA strength was more frequently encountered when directed against haploidentical donors as compared with mismatched unrelated donors. DSA were most commonly detected in female patients directed against their children. Because the presence of DSA has been considered prohibitive for HLA-mismatched alloBMT, we additionally report a desensitization methodology used to reduce DSA to negative or weak levels, ie, levels well below those detectable in a flow cytometric crossmatch. Nine patients without other available donors underwent desensitization. Eight who reduced their DSA to negative or weak levels proceeded to alloBMT and achieved full donor engraftment. These data support routine DSA evaluation in all patients considered for mismatched alloBMT; however, for patients with no other viable options, desensitization to weak or negative DSA levels may afford the opportunity for successful transplantation (read more)